Method of manufacturing semiconductor element

ABSTRACT

A method of manufacturing semiconductor device invented comprises a process of forming a gate electrode ( 5 ) having metallic silicide layer ( 3 ) on a semiconductor substrate, a process of decreasing boundaries of grains on the surface of said metallic silicide layer ( 3 ) at least a portion of which is exposed, and a process of forming spacers comprising oxide film ( 10 ) on the side wall of said gate electrode ( 5 ); in this order; so as to avoid the abnormal oxidation of said metallic silicide layer ( 3 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of manufacturingsemiconductor element, especially, which has metallic silicide layer inits gate electrode.

[0003] 2. Description of the Related Art

[0004] As high integration of semiconductor device proceeds, a demandfor faster and finer element of semiconductor increases. To accept thisdemand, a gate electrode comprising metallic silicide layer is adoptedfor semiconductor element of MOS structure.

[0005] A gate electrode having metallic silicide layer is formed, forexample, as described below.

[0006] At first, an isolation of an element is performed. After this, agate oxide film and a polysilicon film are formed, in this order. Then,a metallic silicide layer is formed on the polysilicon film by PVDmethod or CVD method. And, a SiN layer is formed on the top of gateelectrode with a thermal process using CVD of reduced pressure etc. Thisthermal process is performed at comparatively high temperature of arange of 700° C. to 800° C.

[0007] After forming a SiN layer, a lithography for forming a gateelectrode is performed. And, an etching for forming a gate electrode isperformed with this patterned SiN layer used as a mask. Thus, a gateelectrode is formed. And, after this, the photo-resist used for etchingis removed.

[0008] After removing the photo-resist, oxide films are formed forcovering the side walls of the gate electrode with a CVD method ofreduced pressure etc.

[0009] However, the conventional structure of gate electrode mentionedabove could not sufficiently recover from the damage received during theetching process, for the side wall of gate electrode was covered withoxide film by a CVD method of reduced pressure. And, this is a problemto be solved. Moreover, over-etching of gate oxide film occurs. And, bythis, it becomes impossible to compensate for thinning of gate oxidefilm. As a result, there was another problem of causing leak of gate.

[0010] Therefore, in order to prevent leak of gate, a method ofperforming heat oxidation treatment is generally used. But, in themethod mentioned above, a heat treatment for forming SiN layer wasnecessary. Therefore, the metallic silicide was crystallized. And, thecrystal was in a state that oxygen was likely to diffuse. An oxidationprocess in this state caused increasing oxidation of metal of W etc. andSi. And, expansion of volume occurred. Therefore, difference of stressoccurred between polysilicon and metallic silicide in the lower portionof metallic silicide layer. And, difference of stress also occurredbetween metallic silicide and SiN layer in the upper portion of metallicsilicide layer. As a result, fastening between metallic silicide layerand SiN deteriorated. And, peeling off of SiN layer occurred.

[0011] That is, according to the method mentioned above, a gateelectrode 40 comprising polysilicon layer 42, metallic silicide layer43,and SiN layer 44 was formed. And, when its surface was observed, thestate of surface shown in FIG. 5(b) was recognized. In FIG. 5(b),metallic silicide crystal 45 grew like notches in the horizontaldirection, because the side wall of gate electrode 40 was abnormallyoxidized. And, SiN layer 44 was likely to peel off owing to abnormaloxidation as mentioned above.

[0012] As a method of preventing abnormal oxidation mentioned above, amethod of implanting nitrogen in the side wall of gate electrode 40 hasbeen suggested (c.f. JP 08-321613).

[0013] However, the conventional method has a problem that voids(vacancies) occurred because of nitrogen implanted in the semiconductorsubstrate.

SUMMARY OF THE INVENTION

[0014] Therefore, the present invention aimed at providing a method ofmanufacturing semiconductor substrate which can restrain occurrence ofabnormal oxidation under heat treatment at high temperature afterforming metallic silicide layer.

[0015] The problem mentioned above can be solved, because the presentinvention comprises as next.

[0016] The first is a method of manufacturing a semiconductor elementcomprising:

[0017] a process of forming gate electrode having metallic silicidelayer on a semiconductor substrate,

[0018] a process of decreasing grain boundaries on the surface of themetallic silicide at least a portion of which is exposed, and

[0019] a process of forming spacer consisting of oxide film on the sidewall of gate electrode.

[0020] The second is a method of manufacturing a semiconductor elementaccording to the first method, wherein the process of decreasing saidgrain boundaries is a process of performing heat treatment to saidmetallic silicide layer in an atmosphere consisting of a chief elementof nitrogen gas.

[0021] The third is a method of manufacturing a semiconductor elementaccording to the first method, wherein the process of decreasing saidgrain boundaries is a process of performing heat treatment to saidmetallic silicide layer in an atmosphere consisting of a chief elementof argon gas.

[0022] The fourth is a method of manufacturing a semiconductor elementaccording to the first method, wherein the process of decreasing saidgrain boundaries is a process of performing heat treatment to saidmetallic silicide layer in an atmosphere consisting of a mixture gas ofchief elements of nitrogen and ammonia.

[0023] The fifth is a method of manufacturing a semiconductor elementaccording to the first method, wherein the process of decreasing saidgrain boundaries is performed after performing a reduced pressureprocess.

[0024] These methods has a process of decreasing grain boundaries afterforming metallic silicide layer. So, occurrence of abnormal oxidation inthe side wall of gate electrode can be restrained, even if a process oftreatment at high temperature is performed after the process ofdecreasing grain boundaries.

[0025] Here, the process of decreasing grain boundaries means a processof performing heat treatment to metallic silicide layer at least aportion of which is exposed in an atmosphere of inoxidizable gasconsisted of a chief element of nitrogen, argon, or mixture gas ofnitrogen and ammonia.

[0026] Moreover, for example, a chief element of nitrogen means anatmosphere including more than 99% density of nitrogen gas. Especially,it means a state of atmosphere including less than 100 ppm of oxidizablegas (oxygen gas etc.). Incidentally, other inoxidizable gas can beincluded if the gas mentioned above is a chief element and the densityof oxidizable gas is less than 100 ppm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1(a) to (d) are sectional views of semiconductor element inthe process of an Embodiment of the present invention.

[0028]FIG. 2 is a plan view of the gate electrode formed by the methodof present invention.

[0029]FIG. 3 is a sectional view of the gate electrode formed by themethod of Embodiment 2 of present invention.

[0030]FIG. 4(a) and (b) are sectional views of NMOS-FET having LDDstructure manufactured by the method of present invention.

[0031]FIG. 5(a) is a sectional view of a gate electrode formed by theconventional art, and (b) shows a state of abnormal oxidation of gateelectrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereafter, Embodiments 1 to 4 of the method of manufacturingsemiconductor element according to present invention will be described,referring to the drawings.

EMBODIMENT 1

[0033] The Embodiment 1 of manufacturing method of present inventioncomprises a process of forming a gate electrode having a metallicsilicide layer on a semiconductor substrate, a process of performingheat treatment of said metallic silicide layer at least a portion ofwhich is exposed, in a gas atmosphere consisting of a chief element ofnitrogen (a heat treatment process of metallic silicide layer), and aprocess of forming spacers comprising oxide films on the side walls ofsaid gate electrode; in this order.

[0034] In the concrete, at first, an isolation of an element isperformed, as shown in FIG. 1(a), by the method which is same as theconventional method known in public. After isolating an element, a gateoxide film 1 and a polysilicon layer 2 are formed, as shown in FIG.1(b), by the method shown in public. Then, an ion implantation isperformed so as to introduce impurity to the polysilicon layer 2 to makean electrode from it. And, a metallic silicide layer 3 is formed on thepolysilicon layer 2 by PVD method or CVD method.. Here, the temperaturefor forming the metallic silicide layer 3 is preferably 400° C. to 600°C. After forming the metallic silicide layer 3, a heat treatment whichtemperature is higher than that for forming the metallic silicide layer3 is performed. Here, the temperature of this heat treatment ispreferably 700° C. to 800° C.

[0035] Incidentally, the way of heat treatment is not limited at all.However, the heat treatment can be performed together with a process offorming a SiN layer 4, which becomes a hard mask for forming gate and amask for making self-aligned contact, on the top of the gate electrode.

[0036] In this occasion, the SiN layer 4 is preferably formed by CVDmethod of reduced pressure, which can make a minute film with little Hincluded. The heat treatment by this CVD with reduced pressure isperformed at a temperature higher than the temperature for forming themetallic silicide layer 3.

[0037] After forming the SiN layer 4, a photolithography for forming agate electrode 5 is performed, as shown in FIG. 1(c). And, an etchingfor forming gate (process of forming gate electrode) is performed. Bythis gate etching, side walls of the portions of metallic silicide layer3 are exposed.

[0038] After forming the gate electrode 5, it gets a heat treatment(process of heat treatment of metallic silicide layer) is performed.This is performed in a gas atmosphere including nitrogen as a chiefelement, in a chamber of heat treating apparatus (RTA) purged withnitrogen for example.

[0039] The temperature of heat treatment in the heat treatment processof metallic silicide layer is preferably 700 to 800° C. in a view pointof decreasing grain boundaries of silicide crystal without fail. Theprocess time is preferably 30 to 40 sec. in the same point of view.

[0040] Since the gas atmosphere in the chamber consists of a chiefelement of nitrogen, the gas atmosphere consists of little oxidizablegas. That is, the density of oxidizable gas in the atmosphere is lessthan 100 ppm. Therefore, diffusion of oxygen in the metallic silicidelayer 3 is contained. And, abnormal oxidation can be prevented.Moreover, grain boundary of silicide crystal in the side wall becomesless. So, diffusion of oxygen or moisture after forming gate can beprevented.

[0041] Moreover, nitrogen gas is convenient for manufacturing devices,because it is not expensive and easy to use.

[0042] After performing heat treatment in the process of treatingmetallic silicide layer with heat, an oxidizing treatment is performedin a common furnace. By performing this oxidizing treatment, as shown inFIG. 1(d), spacers comprising oxide film 10, 10 are formed on the sidewalls of polysilicon layer and tungsten silicide layer, and on the gateoxide film. Incidentally, these spacers are used as a mask layer forforming an LDD (Lightly Doped Drain) structure, and as a protectionlayer for protecting the side walls of gate electrode.

[0043] In the heat treatment mentioned above, the atmosphere forperforming heat treatment can include either oxygen or oxygen withmoisture, because diffusion of oxidizing substance in the metallicsilicide layer is restrained. Moreover, in order to obtain a preferablethickness of an oxide film, the atmosphere, process temperature, processtime, gas flow quantity etc. can be set voluntarily.

[0044]FIG. 2 shows a state of top surface of the gate electrode 5 formedby the manufacturing method of Embodiment 1. In FIG. 2, what is formedvertically in the central portion of the figure is the gate electrode 5.Moreover, what is formed at each side of the gate electrode 5 is thegate oxide film. As apparently shown in FIG. 2, abnormal oxidationresulting in deposition of notched crystal described referring to FIG.5(b) does not come out on the side walls of gate electrode 5. That is,by the manufacturing method of present invention, the side wall of gateelectrode is oxidized uniformly without any abnormal oxidization.

[0045] As described above, according to the manufacturing method ofEmbodiment 1, abnormal oxidation can be prevented when the side wall isoxidized after forming gate electrode, in any condition such asatmosphere (only oxygen or with moisture), process temperature, processtime, gas flow quantity etc.

EMBODIMENT 2

[0046] The manufacturing method of Embodiment 2 of present inventioncomprises a process of forming a gas electrode having a metallicsilicide layer on a semiconductor substrate, a process of performingheat treatment of the metallic silicide layer at least a portion ofwhich is exposed in an atmosphere consisting of a chief element of argongas, and a process of forming spacers comprising oxide film on each sideof the gate electrode; in this order.

[0047] The manufacturing method of Embodiment 2 is same as themanufacturing method of Embodiment 1 except the process of treatingmetallic silicide layer with heat; wherein the chief element of gasatmosphere for heat-treatment is not nitrogen, but argon.

[0048] That is, after forming a gate electrode 5 as well as themanufacturing method of Embodiment 1, heat-treatment in an atmosphere ofchief element of argon gas is performed in a chamber of heat-treatingapparatus (RTA) purged with argon gas. Here, chief element of argon gasmeans that the density of argon in the gas atmosphere is not less than99%. And, especially, the density of oxidizable gas (oxygen gas etc.) isnot more than 100 ppm.

[0049] In an atmosphere of chief element of argon gas, abnormaloxidation can be prevented as well as nitrogen gas. Moreover, a methodby using argon gas of Embodiment 2 is profitable in the occasion whennitrization of source region or drain region of the semiconductorsubstrate must be avoided.

[0050] Incidentally, process temperature, process time etc. ofheat-treatment condition is same as manufacturing method of Embodiment1.

[0051] And, spacers comprising oxide film is formed on the side wall ofgate electrode as same as Embodiment 1, after performing heat-treatingprocess of metallic silicide layer, which is performed in the argon gasatmosphere of chief element.

EMBODIMENT 3

[0052] The manufacturing method of Embodiment 3 comprises a process offorming a gate electrode having a metallic silicide layer on asemiconductor substrate, a process of performing heat-treatment in anatmosphere of chief element of mixture gas consisting of nitrogen andammonia, and a process of forming spacers comprising oxide film on theside wall of the gate electrode; in this order.

[0053] The method of Embodiment 3 is same as Embodiment 1 except theheat-treating process of metallic silicide layer, wherein theheat-treatment in a gas atmosphere of chief element is not nitrogen butmixture gas of nitrogen and ammonia.

[0054] At first, a gate electrode 5 is formed as same as Embodiment 1.After this, a chamber is purged with nitrogen gas so as to make thedensity of oxidizable gas less than 100 ppm. Subsequently, the wafer islet in the chamber of heating apparatus so as to heat it with lamp.

[0055] In the meantime, the wafer is heated up to a prescribedtemperature. Then, ammonia gas is introduced into the chamber. And, anatmosphere of mixture gas consisting of nitrogen and ammonia is made.Then, a heat-treatment is made. The temperature in this occasion ispreferably not less than 650° C. And, it is still preferable if it is700 to 800° C.

[0056] The density of ammonia gas in the atmosphere is preferable if itis 1 to 3% provided that the nitrified region mentioned later is formedin a reasonable range.

[0057] And, spacers comprising oxide film is formed on the side wall ofgate electrode as same as Embodiment 1, after performing theheat-treating process of metallic silicide layer, which is performed inthe atmosphere of mixture gas of chief elements of nitrogen and ammonia.

[0058] According to the method of Embodiment 3, abnormal oxidation onthe side wall does not occur. And, as shown in FIG. 3, nitrified region7 is formed in a range of side wall to the bottom portion of metallicsilicide layer 3 assisted by the ammonia gas. Therefore, nitrogen ofhigh density is introduced into the oxide film on the substrate exceptthe portion under gate electrode 5. As a result, diffusion of impuritiesfrom the substrate to the spacers formed on the side wall of gateelectrode 5 can be prevented.

[0059] After performing heat-treatment mentioned above, oxidizingtreatment is performed in a common oxidizing furnace as same asEmbodiment 1. The gas let in the furnace as an atmosphere in thisoccasion preferably consists of a chief element of nitrogen. In themeantime, the furnace is heated up to a preferable temperature.Subsequently, a gas for oxidizing is introduced there.

[0060] This gas may consist of oxygen or moisture.

EMBODIMENT 4

[0061] The method of Embodiment 4 of present invention comprises aprocess of forming a gate electrode having a metallic silicide layer ona semiconductor substrate, a process of performing heat-treatment of themetallic silicide layer at least a portion of which is exposed in anatmosphere of a chief element of nitrogen gas (heat-treating process ofmetallic silicide layer), and a process of forming spacers comprisingoxide film on the side wall of gate electrode; in this order; whereinthe heat-treating process of metallic silicide layer is performed aftera process of performing reduced pressure treatment (reduced pressuretreating process).

[0062] In the concrete, at first, etching for forming gate is performedas same as Embodiment 1. After etching for gate, the photoresist usedfor etching is removed. And, a gate electrode is formed. After this, thereduced pressure treating process is performed by using low pressure CVDdevice for example. Subsequently, a heat-treatment in an atmosphere ofchief element of nitrogen gas is performed as same as Embodiment 1.

[0063] The reduced pressure treatment is performed by taking thesemiconductor substrate formed the gate electrode in the furnace at itstemperature of less than 550° C.

[0064] By performing the reduced pressure treatment, the density ofoxygen on the surface of wafer (density of oxidizable gas) can be madeless than 100 ppm.

[0065] After performing reduced pressure process, the wafer is heatedup. And, heat treatment in atmosphere of a chief element of nitrogen gasat 700 to 800° C. is performed as same as Embodiment 1 (heat treatingprocess of metallic silicide layer).

[0066] In this occasion, if the wafer is heated up without performingreduced pressure process, abnormal oxidation occurs, because the densityof oxygen between wafers is high.

[0067] The pressure of reduced pressure process is preferably 13 to 65Pa.

[0068] After performing heat treatment of more than 650° C., the waferis cooled down to the process temperature or inletting temperature.Then, the wafer is taken out. After this, spacer comprising oxide filmis formed on the side wall of gate electrode as same as Embodiment 1.

[0069] According to Embodiment 4, the density of oxidizable gas isefficiently decreased. Moreover, heat treating process of metallicsilicide layer after reduced pressure process can be performed inprocessing apparatus, which can process a batch of wafers. Therefore,productivity can increase.

[0070] Next, an example of manufacturing method of NMOS-FET having LDDstructure is described referring to FIG. 1 and FIG. 4.

[0071] At first, as mentioned before in the description with FIG. 1(a)to FIG. 1(c), gate electrode 5 (generally polysilicon) is formed on thesemiconductor substrate 1. Next, as shown in FIG. 4(a), phosphorus isintroduced by ion implantation using the gate electrode 5 as a mask. Bythis, shallow n− layer 50 is formed all over the source and drain regionof semiconductor substrate 1.

[0072] After this, as shown in FIG. 4(b), oxide film 10 (side wall) isformed on the side wall of gate electrode 5.

[0073] This oxide film 10 is formed with the condition mentioned before(condition described in Embodiments 1 to 4). By this, gate electrodewith restraining abnormal oxidation can be formed.

[0074] After forming oxide film 10, arsenic is introduced by ionimplantation using oxide film 10 and gate electrode 5 as a mask. Bythis, deep n+ layer 70 is formed in the portion of source and drainregion distant from the gate electrode 5. After this, wiring etc. isperformed. Then, NMOS-FET of LDD structure is manufactured.

[0075] Incidentally, the manufacturing method mentioned above is notonly applied to NMOS-FET but also applied to various semiconductorelements such as CMOS-FET etc.

[0076] And, the present invention is not limited to Embodiments 1 to 4.

[0077] For example, the material of metallic silicide layer is notlimited to Tungsten silicide, which is preferable in practical use. Thatis, molybdenum silicide or titanium silicide etc. is available.

[0078] Moreover, if the heat treatment after forming metallic silicidelayer is performed at a temperature higher than the temperature offorming metallic silicide, SiN layer formed by reduced pressure CVDmethod is not always necessary.

What is claimed is:
 1. A method of manufacturing a semiconductor elementcomprising: a process of forming gate electrode having metallic silicidelayer on a semiconductor substrate, a process of decreasing grainboundaries on the surface of the metallic silicide at least a portion ofwhich is exposed, and a process of forming spacer consisting of oxidefilm on the side wall of gate electrode.
 2. A method of manufacturing asemiconductor element according to claim 1, wherein the process ofdecreasing said grain boundaries is a process of performing heattreatment to said metallic silicide layer in an atmosphere consisting ofa chief element of nitrogen gas.
 3. A method of manufacturing asemiconductor element according to claim 1, wherein the process ofdecreasing said grain boundaries is a process of performing heattreatment to said metallic suicide layer in an atmosphere consisting ofa chief element of argon gas.
 4. A method of manufacturing asemiconductor element according to claim 1, wherein the process ofdecreasing said grain boundaries is a process of performing heattreatment to said metallic silicide layer in an atmosphere consisting ofa mixture gas of chief elements of nitrogen and ammonia.
 5. A method ofmanufacturing a semiconductor element according to claim 1, wherein theprocess of decreasing said grain boundaries is a process of performingheat treatment to said metallic silicide layer in an atmosphereincluding oxidizable gas less than 100 ppm.
 6. A method of manufacturinga semiconductor element according to claim 1, wherein said metallicsilicide is tungsten silicide and the process of decreasing said grainboundaries is a process of performing heat treatment at temperature of700 to 800° C. for time of 30 to 40 sec.
 7. A method of manufacturing asemiconductor element according to claim 1, wherein said metallicsilicide is tungsten silicide and the process of decreasing said grainboundaries is a process of performing heat treatment in an atmosphereincluding ammonia of 1 to 3%.
 8. A method of manufacturing asemiconductor element according to claim 1, wherein the process ofdecreasing said grain boundaries is performed after performing a reducedpressure process.
 9. A method of manufacturing a semiconductor elementaccording to claim 1; wherein the process of decreasing said grainboundaries is a process of heat treatment to said metallic silicidelayer in an atmosphere including oxidizable gas, and performed afterperforming a reduced pressure process of making the oxidizable gas lessthan 100 ppm.
 10. A method of manufacturing a semiconductor elementaccording to claim 1, wherein said metallic silicide is tungstensilicide and the process of decreasing said grain boundaries is aprocess of heat treatment performed at temperature 700 to 800° C. andperformed after performing a reduced pressure process performed atpressure of 13 to 65 pa.